Jet engine exhaust noise suppression



United States Patent Inventors Henry T. Nagamatsu Schenectady; Russell E. Sheer, Jr., Cohoes, New York [21] Appl. No. 846,493 [22] Filed July 3 1 i969 Continuation-impart of Ser. No. 664,708, Aug. 31,1967, abandoned [45] Patented Oct. 20, 1970 [73] Assignee I GeneralElectr-icCompany a corporation of New York [54] JET ENGINE EXHAUST NOISE SUPPRESSION 8 Claims, 6 Drawing Figs.

52 US. Cl 181/51, 239/1 27.3, 239/265. 19 [51] Int. Cl 864d 33/06,

F0 1 n 33/02 [50] Field ofSearch l8l/33,43, 5i, 33.22l, 33.222, 33.22; 239/127.3, 265.19

[56] References Cited UNITED STATES PATENTS 2,936,578 5/1960 Chamberlain 239/265. l9

Primary ExaminerRobert S. Ward, Jr.

' AttorneysPaul A. Frank, John F. Ahern, Julius J.

Zaskalicky, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT: An array of rods and a shroud'coact on a jet issuing from a nozzle at supersonic velocities to substantially reduce the noise emitted beyond the reduction obtainable due to the recited elements taken singly. The rods in the array are radially oriented with respect to the axis of the jet in the maximum velocity region and are uniformly displaced circumferentially about and radially from the axis of the nozzle. The

shroud is axially aligned with the noule and spaced therefrom to permit ambient air to be aspirated into the shroud and mix with the exhaust from the nozzle.

cooooooooo: ,oooenoeooom, 'ocooonoooo' Patented 0a. 20,- 1970 3,534,831

Sheet 1 of 2 a a n a R Q,

/ J// ///7Il Inveht 01 3. Henry Z'figgamatsu, Russel/Z 5. cer;

1 JET ENGINE EXHAUST NOISE SUPPRESSION This application is a continuation-in-part of our copending application Ser. No. 664,708, filed Aug. 3 l 1967, now abandoned, and assigned to the assignee of the present invention.

The invention described and claimed in the United States patent application herein resulted from work done under United States Government contract FA-SS- 66-6. The United States Government has an irrevocable nonexclusive license under said application to practice and have practiced the invention claimed herein including the unlimited right to sublicense others to practice and have practiced the claimed invention for any purpose whatsoever.

The present invention relates to the suppression of noise produced by the exhausts emitted from the propulsive nozzle ofa supersonic jet engine.

The advent of aircraft of larger size and of higher speed capability has concomitantly resulted in an increase in the level of noise emitted therefrom. The increase in the level of noise has been primarily produced by the increase in thrust and in velocity of the hot gas streams discharged'fr'om the propulsive nozzle thereof. The level of noise so generated has reached a point which has caused increasing concern particularly in connection with low altitude flight and in the vicinity of airports and brought onrequirements for the reduction thereof.

It is a principal object of the present invention to provide means to reduce substantially the noise generated by the exhaust emitted at supersonic velocities from the propulsive nozzle of a jet engine.

It is another object of the present invention to provide noise suppression means for a supersonic jet engine which produces minimal degradation of thrust.

It is a further object of the present invention to provide noise suppression means for a jet engine which is retractable.

In accordance with an illustrative embodiment of the present invention there is provided an axisymmetrical nozzle having an inlet end and an exhaust end, and meansfor applying a gas under pressure to the inlet end to produce a flow of gas at supersonic velocities from the exhaust end. Obstructions to fluid flow are provided adjacent the exhaust end in the region of maximum velocity of the flow for slowing the flow of fluid from the exhaust end. The obstructions which may be in the form of rods are located in a plane perpendicular to the longitudinal axis of the nozzle and uniformly displaced circumferentially about and radially from the intersection of the axis with the plane. The obstructions are so constituted and oriented to produce a reduction in velocity of flow which is substantial and which is symmetrical with respect to the axis. A cylindrical shroud axially aligned with the axis of the nozzle and having an inlet spaced from the exhaust end of the nozzle is also provided. The internal diameter of the shroud is sub stantially larger than the diameterof the exhaust end of the nozzle to induce a large mass of ambient flow into the inlet of the shroud to mix with the flow from the exhaust end of the the velocity of the flow emerging at the outlet of the shroud.

The novel features which are believed to be characteristic of the present invention are set forth in the appended claims.

The invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 shows a supersonic jet nozzle in cross section with rods located adjacent the exhaust end thereof.

FIG. 2 shows an end view of the nozzle of FIG. '1.

FIG. 3a shows the outline of the exhaust from the nozzle of 3 FIG. 1, without rods attached thereto, perpendicular to the longitudinal axis of the nozzle.

FIG. 3b shows the outline of the exhaust from the nozzle of FIG. 1 perpendicular to the longitudinal axis thereof.

' 13 connected by a passageway 14 generally circular'incross section. The passageway is convergent from the inlet end 12 to the throat 15 of the nozzle and thereafter is divergent to the exhaust end 13. Gas under pressure developed by the jet engine is applied to the inlet end 12 and produces a flow of gas at supersonic velocities from the exhaust end 13.

To the exhaust end of the nozzle 10 in the 'region of maximum velocity of the exhaust therefrom is secured a ring 20 on which are located a plurality of projections 21, shown as rods of circular cross section. The rods 21 extend radially inward towardthe axis 22 of the noule 10. The rods 21 are uniformly displaced circumferentially about the ring 20 and radially extend for a short distance into the path of the exhaust from the exhaust end 13. The rods 21 extend uniformly in the radial direction. Such structure not only effectively reduces the velocity of the jetexhaust but does it in a uniform manner in a plane perpendicular to the axis of the nozzle. Location of the rods 21 in the high supersonic velocity region has a maximum effect in producing shock waves in the exhaust. Such shock waves bring the sonic velocity region of the exhaust considerably closer to the exhaust end of the nozzle and concurrently produces good mixing of the exhaust with ambient air.

Further velocity reduction of the exhaust and elimination of large velocity gradients in the exhaust is provided by a shroud to be described below in connection with FIG. 4. The crosssectional pattern 25 of the exhaust from the nozzle in a plane perpendicular to the axis of the nozzle in the absence of the projections is such as shown in FIG. Be. With the projections attached, the cross-sectional pattern 26 of the jet exhaust has u'sculloped or undulating shape as shown in FIG. 3/). More effective mixing of the exhaust gases with the ambient air is achieved when the pattern of flow is as shown in FIG. 3b. The

nozzle with projections attached shown in FIGS. I and 2 is incorporated in the embodiment of FIG. 4 with certain modifications and additions.

In FIG. 4, to which reference is now made, elements identical to the elements of FIGS. 1 and 2 are designated by the same symbol. In FIG. 4, the radially oriented rods 21 are adjustable by any adjusting means 30. In addition, a shroud 31 isprovided. The shroud is cylindrical in form and is axially aligned with the axis of the nozzle. The shroud 31 hasan inlet end 32 and an outlet end 33. The shroud 31 is supported by In operation of the nozzle 10 with the noise suppression 1 means associated therewith described above, gas under pressure from a jet engine is applied to the inlet of the nozzle to produce an exhaust therefrom of supersonic velocity. The rods 21 act on the exhaust to produce shock waves which reduce the overall velocity of the exhaust gases and at the 7 same timefacilitate mixing of such exhaust gases with the ambient air, the flow of which is indicated by flow lines 36. Such mixing also facilitates aspiration of ambient air in the shroud. Further mixing of the exhaust and ambient air takes place within the shroud 31 and produces a further reduction in velocity of the exhaust and also brings about a greater uniformity of flow in a plane perpendicular to the longitudinal axis of the shroud. The latter action is enhanced by the symmetrical shock wave pattern produced by the rods '21. The

shroud 31 is made sufficiently long so that not only are the exhaust gases reduced to velocities significantly below sonic velocities but that such velocities'also are uniform at the outlet end 33 of the shroud in a plane perpendicular to the longitudinal axis thereof. It has been found that the noise reduction resulting from the utilization of the projections in the high velocity region of the exhaust in conjunction with a shroud of adequate length is considerably beyond the simple addition of the noise reductions which would be produced by the rods alone and by the shroud alone.

While a length of shroud of the order of twice the diameter of the exhaust end of the nozzle is effective in accordance with the present invention, longer lengths are preferred, if practi-' tion from supersonic to sonic velocities has been brought close to the exhaust end by the rods and as the portion of exhaust from the exhaust end to the point of transition generates a major portion of noise, the provision of shroud encompassing such portion also aids significantly in confining such noise. The latter action is aided by the sound absorbing material 37 such as porous asbestos or stainless steel wool attached to the forward inside surface of the shroud.

The embodiment of HO. 5 is similar to the embodiment of FIG. 4 and elements of FIG. 5 identical to the elements of FIG.v

4 are designated by the same symbol. In the embodiment of FIG. 5, the obstruction to the flow of exhaust gases from the exhaust end 13 of the propulsive nozzle is provided by a plurality of auxiliary nozzles 40 in place of the rods 21 used in FIG. 4. The ring 20 is provided with a plurality of such auxiliary nozzles 40 uniformly spaced circumferentially about the ring 20, conveniently six such auxiliary nozzles may be used in place of the six rods shown in FIG. 2. The auxiliary nozzles 40 are oriented to produce a plurality of streams of fluid each radially oriented with respect to the axis of the nozzle and the exhaust. Each of the auxiliary nozzles 40 is provided with a respective feed line 41, one end of which is connected to the auxiliary nozzle 40 and the other end is connected to a high pressure region on the upstream side of the throat of the nozzle 10. A valve 42 means may be located in each of the supply ducts 41 for the auxiliary noules to control the flow of fluid from the upstream end of the propulsive nozzle 10 into the auxiliary nozzle 40 to provide a symmetrical reduction of velocity in a plane perpendicular to the axis of the nozzle. It has been found that a bleed flow of about 2 percent of the flow into the auxiliary nozzles is adequate for providing adequate obstruction in the high velocity region of the exhaust from the propulsive nozzle 10 to produce the sound reduction effects mentioned above in connection with FIGS. 1 and 4 with being located adjacent said outlet end in the region of maximum velocity of said flow, said means being located in a plane perpendicular to the axis of said-nozzle, said means producing a reduction in velocity of said flow which is substantial and which is symmetrical with respect to said axis; and

a cylindrical shroud axially aligned with the axis of said exhaust' end and having an inlet and an outlet end, the inlet end of said shroud being adjacent to the outletend: of said nozzle and spaced therefrom, the internal diameter of said shroud being substantially larger than the diarneter of said outlet end of said nozzle to induce a large mass of ambient flow into the inlet end of said shroud to mix with the flow from said outlet end of said nozzle as affected by said means for obstructing the flow of fluid, the length of said shroud in the axial direction being of an extent to provide thorough mixing of said flow from said outlet end of said nozzle with said ambient flow to reduce substantially the velocity of the flow emerging at said outlet end of said shroud and to produce substantially uniform velocity thereat, whereby the noise emanating from the flow emerging from said outlet end of said shroud is substantially reduced.

2. The combination of claim 1 in which said means for slowing the flow of fluid from said outlet end of said nozzle includes a plurality of projections extending radially into the flow from said outlet end, said projections lying in said plane and uniformly displaced circumferentially about and radially from the intersection of said axis with said plane.

3. The combination of claim 2 in which said projections are tabs.

4. The combination of claim 2 in which said projections are rodlike elements.

5. The combination of claim 2 in which said projections are 7. The combination of claim 6 in which said auxiliary nozzles are supplied with a small percentage of the fluid flowing in said nozzle from the upstream end thereof.

8. The combination of claim 1 in which a sound deadening material is secured to the forward end of the inner cylindrical surface of said shroud. 

